An Ethernet Virtual Private Network (EVPN) may be used to extend two or more remote layer two (L2) customer networks through an intermediate layer three (L3) network (usually referred to as a provider network), in a transparent manner, i.e., as if the intermediate L3 network does not exist. In particular, the EVPN transports L2 communications, such as Ethernet packets or “frames,” between customer networks via the intermediate network. In a typical configuration, provider edge (PE) network devices (e.g., routers and/or switches) coupled to the customer edge (CE) network devices of the customer networks define label switched paths (LSPs) (also referred to as pseudowires) within the provider network to carry encapsulated L2 communications as if these customer networks were directly attached to the same local area network (LAN). In some configurations, the PE network devices may also be connected by an Internet Protocol (IP) infrastructure in which case IP/Generic Routing Encapsulation (GRE) tunneling or other IP tunneling can be used between the network devices.
EVPN may be combined with Provider Backbone Bridging (PBB) defined in accordance with IEEE standard 802.1ah. PBB defines an architecture and bridging protocols in which a Provider Backbone Bridged Network (PBBN) provides L2 connectivity between multiple provider bridge networks (PBNs) of one or more different network service providers. Such large area L2 network connectivity may be deployed, for example, in metropolitan area networks. Each PBN provides one or more service virtual LANs (“S-VLANS”) to service and isolate L2 traffic from customer networks. Access switches for the PBBN typically include a set of Backbone Edge Bridges (BEBs) that interconnect some or all of the S-VLANs supported by multiple PBNs. Each BEB provides interfaces that further encapsulate L2 frames for transport through the PBBN. The VLANs used to encapsulate L2 frames from the PBNs and transport the L2 traffic through the PBBN are known as backbone VLANs (B-VLANs), and the resources that support those VLANs are usually considered to be part of the PBBN. In this way, the PBBN may be referred to as a Virtual Bridged Local Area Network under the administrative control of a backbone provider. PBB-EVPN combines functionality of an EVPN and PBB BEB bridge, such that Multi-Protocol Label Switching (MPLS) LSPs defined in an EVPN are mapped to PBB encapsulated traffic.
In a PBB-EVPN, a set of PE routers may operate in a common Ethernet Segment in active-active mode with all PE routers forwarding network traffic in the Ethernet Segment. One of the PE routers in the Ethernet Segment may operate as a designated forwarder (DF) to forward Broadcast, Unknown Unicast, and Multicast (BUM) traffic while the other PE routers in the Ethernet Segment drop BUM traffic. The Ethernet Segment may also be associated with a Backbone Media Access Control (B-MAC) address, which is used by remote PE routers to forward network traffic through a service provider network to the set of PE routers included in the common Ethernet Segment. In some examples, a remote PE router may forward a known unicast packet to a particular non-DF PE router that is associated with the B-MAC address. Although the remote PE router may have already learned the destination Customer-MAC (C-MAC) thereby causing the remote PE router to send the network packet as known unicast traffic, the particular PE router may not have yet learned the C-MAC address. As such, although the particular PE router may include a path via the Ethernet Segment to forward the network packet to its destination, the particular PE router may treat the known unicast traffic as BUM traffic (i.e., drop the traffic) because the particular PE router does not recognize the C-MAC address and the particular PE router is not the DF.